T28 Gear Door Follow-up

If any of you have been following my blog, you know that I had issues with my Airfield/FMS 1400mm Trojan T28 electrical system.  In blog post T28 update and putting test equipment to good use the result was a smoked front landing gear door servo.  In this post, I'll review what I did to fix this as it did not turn out to be as easy as it seemed.

On the outset, it looked like all I needed to do was to replace one servo and be done with it.  Such was not the case.  Not only did I need to source a replacement servo, but I still needed to make sure that what blew the first servo would not destroy the replacement.

Sourcing a replacement servo did not initially seem like a big deal as when I removed the original, it looked to be the same size as the cheep HK servos I already had.  The only difference that I could see was the the mounting flanges were slightly off, with the original black plastic servo sitting a little lower (one, maybe two, mm).

This did not turn out to be that big of a deal and pretty soon I had the replacement in.  I had already centered the servo and so I just screwed the servo arm in place at a 90 deg. angle, facing inboard, as the original was.  Then I hooked up the linkage, in what seemed like a neutral setting.  I then plugged it into the sequencer.  Then I plugged the sequencer into into my servo tester.  And finally, a battery pack into the servo tester to power everything.

Suddenly everything is going wonky!  The doors are closing and the landing gear is cycling down!  I reverse the servo tester and then the landing gear is retracting before the doors are opening.  Dog gone it!  I pulled the power.

What the heck is going on!?!

After some research on the Internet, I find out that the sequencer and my wiring are not messed up, but the front landing gear door servo needs to be reversed!

Out it comes again.

I don't want to wait and order just one reversed servo.  Especially as I'm not even ready for another parts order.  So, online I go again for more research and find a couple of good videos on how to reverse a servo.  Since I have a background in electronics and am proficient at soldering, I decide to tackle it.

An hour or so later (I took it slow to make sure I had it right), I had a reverse servo ready to go (sorry, but I don't have any photos of this).

Back in it goes and I'm ready to test.  Servo to sequencer, sequencer to servo tester, servo tester to battery pack.....and...phew!  All is working fine and the doors and landing gear are sequencing as they should!

A little adjusting of the linkage and the doors are closing flush and appear to be opening fine.  I can hear a little servo noise with everything sequenced open, but don't think too much as it seems like that is the norm with servos today.

Now, knowing that this is not the end, I add my servo and system power meter into the mix (check out this post on how I made this meter: Can't get enough test equipment).  Low and behold, I'm pulling similar amp readings as when the original servo blew (over 1 amp!)  I notice that this is when everything is sequenced open and when the servo is making noise.  This is not just some stray noise.  This is a jammed servo.  No wonder the original blew out.

This is the original servo and arm position when closed.

I studied and studied the linkage and servo movement.  The door linkage did not need to move as far as the servo was trying to make it go and could not move that far.  I tried moving the pin in the servo arm in one hole, but then it did not have enough throw and the doors would not open far enough.  What to do?

I thought about using my programmable radio to just reduce the throw, or end limits, of that servo, but with the sequencer in the mix, that would not work.  No way was I going to try to set this up without using the sequencer.

The more I looked at it, the more frustrated I was getting.  There had to be something to do.  Then I looked again at the linkage and how the main push rod from the servo was slender and maid of spring steel, and how it had some flex to it.  Then I remembered mechanical equipment that I had worked on in the past with levers connected to push rods, and how they would lock into place by essentially going past top dead center.  Now any force on the lever (or servo arm in this case) is back toward the shaft and not back on the gears.  That is what I would do.  I set the arm position a few notches forward on the servo, adjusted the linkage so the doors would be closed in that position.  With the doors unhooked, I watched as I sequenced the door servo.  Sure enough, it went up to dead center on its rotation, compared to the link, flexing the push rod as it did.  It came to rest with a little push rod flex but no strain noise from the servo!  I tested it several more times and then connected the doors again.  All was working well.

It felt good to resolve a problem and find a solution that I was happy with.

To help out with visualizing what I did, I added some pictures and a video below.

End position

Start position

The left photo shows the starting point and the right photo shows the end point of the arm travel.  With the arm in this position, any pressure on the arm is straight back and not on the gears.

Please excuse the condition of the plane in these pictures and video as they were not taken after the repair, but after a subsequent crash that bent the front landing gear (that repair might be in a future blog entry).

While it was apart, I used this opportunity to take the pictures and video that I had not done before.

Some lessons learned:
If servos are making noise, check it out and make sure its not because they are jammed or stressed.
If you are replacing a blown servo, find out why.
If you run into a problem, relax and keep at it, and make use of the wisdom out there on the Internet.
And most of all, remember that this is supposed to be fun, enjoyable, and relaxing.

Thanks for stopping by my blog.  Please feel free to post comments, good or bad, and be sure to come back and check for future posts.

Richie's Birthday Party Fly-in

Have you ever wondered what to do for a birthday party for an RC enthusiast?  Have you ever wondered what to give an RC enthusiast?  It can be tough to figure out.  Especially when they are over 16.  Everybody likes to have fun with their friends and family, so what better to do than have a birthday party fly-in with your family and RC enthusiast friends.

This is what Richie's wonderful wife did for him.  She secretly notified all of his flying friends at Sacramento Area Parkflyers and organised a BBQ surprise at the Bilby flying area.  This is a little bit of the RC Flying Fun that we had thanks to Richie and his wife.

Shaky Dave really puts Richie's birthday wing through its paces, and how!

Not just aircraft, but cars too!  Squishy let's a couple of the guys try out his sic fast RC Ferrari before he smokes it's electronics.

A bunch (6?) of planes really put on a show with no collisions!  These guys know their stuff when it comes to piloting these wings.  I think that Dr. Bob as become one of the best and as far as I know he has only been at it with the wings since last summer.

Time to leave and everyone wants to get a last flight in.  Stu gets the walk of shame twice! Ouch.  I had to point this out since he called me on a failed take off and had to walk out to fix it.  There's no film of my fail cause, well, too difficult to film myself.   Richie is rightly proud of one of his new wings and touts its durability.  Supposed to be one last quick flight, yeah right!  Things wind down with Dr. Bob and Shaky Dave comparing motors.


As you can see, if you have the need to throw a birthday party or any sort of event for an RC enthusiast, then get a bunch of their RC flying buddies together at a good flying field with good food (preferably BBQ) and let the fun begin.

Thanks for stopping by my blog.  Please feel free to post comments, good or bad, and be sure to come back and check for future posts.

Fun With My SAP Buds at Bilby

Now, before you get a little upset that I may be being rude about my friends, let me make it clear that I mean my Sacrament Area Parkflyer buds.  You can check us out and get some more information about where we commune and fly at this site parkflysac.com.

I went out to my favorite flying area to have some RC flying fun (I like the Bilby site because it's the closest to me) and hit a snag.  I was in such a hurry to get out there that I forgot the wing spar for the one airplane I brought!  Since I could not fly, I decided to video those that were out there and record the fun and commerrodery.  The video isn't great because all I had with me was my cell phone, but I think you will enjoy them anyway.

In this video a nice 4 stroke 3D plane has problems with stalling before take off as a nice foam jet comes in for a landing.  While waiting for the 3D plane to take off, Dr Bob gets ready and tosses up an insanely speedy little wing of his and puts it through its paces.

In this video the 3D 4 stroke comes in for a nice landing while Richie is getting ready to take off his big wing with landing gear.  It's a big heavy wing so he gives himself a lot of run way.  Those of us parked at then end are grateful for the courtesy.  Surprisingly it takes off quickly. It wobbles around quite a bit but Richie soon takes control and flies it quite nicely.  Then someone gets ready to maiden their Apprentice but is troubled with steering issues.

In this video, a really cool foam jet takes of.  This is the same foam jet that landed in a previous video.  No, this video is not out of order, this is another flight.  It took some distance to take off and from my angle, it almost looked like it was going to end up in the back of my Jeep.

This next video starts with a really nice flyby from the foam jet that took off in the last video.  Just after if flew by, Richie landed his big wing with landing gear.  Unfortunately he came down a little heavy and collapsed the nose wheel.  We take a closer look while the foam jet makes some sweet flybys.  After a few more low and casual passes he comes in for a nice landing.

Dr Bob takes out another screamer.  Too bad about 3/4 of the way through while going vertical, the motor screws come loose and the prop catches the right side of the prop slot.  You can hear this in the video.  The result is that the torque causes the motor to spin and rip all of the motor wires out!  Despite this, Dr Bob deftly brings in this wing with a nice glide and drops it right at his feet.




Quite often we have someone maiddening their new plane.  That is the case with this beautiful new WW2 biplane.  Unlike the Apprentice earlier, this one actually gets a chance and flight.  Let's see what happens.

Yeah, OK, I don't know what happened, but needles to say, it didn't last too long.  He'll get a lot of help and make another attempt soon.

We have a lot of fun out here and also at the other sites around the Sacramento area.  Come out and join us, the more the merrier.  There are no fees or dues, we just ask that everyone fly and behave respectfully and also take care of the areas we fly at.

Hope to see you out there!

Thanks for stopping by my blog.  Please feel free to post comments, good or bad, and be sure to come back and check for future posts.

New Project!

I have a new project that I am very excited about.  I have started scratch building a semi-scale Yak 52.  Now you may be asking, "Why scratch building?", "What is this semi-scale thing?", and "Why the heck a Yak 52?".  Well, let me start off with the easy one. What is semi-scale?  I've come to find out that in modeling this generally refers to something that is built like something but not exactly, and usually built larger or smaller than the original.  So, for my project, I started with drawings and pictures that I got from the Internet.  These drawings and pictures, though reasonably accurate, are not to scale.  In my project I have taken one of the drawings and "scaled" it up to the size I want to build.  So, although I have accurately scaled it up from a drawing, the drawing was not accurately scaled to begin with.  Clear as mud?

Flite Test swappable Nut Ball airplanes my daughter and I built

Why scratch built?  Well, I have enjoyed modding my existing planes and building some simple scratch built foamies like the ones at Flite Test (Check them out they do some really cool stuff with DollarTree foam board).
Then I hooked up with Daniel Madrigal on YouTube.  Check out his site!  This guy builds some really cool foamie jets completely from scratch.  Now I have the bug and I want to move on to my own scratch built planes.


On to the big question that everyone has, why the heck a Yak 52?  Yes, we can all see building a Yak 54, these planes are all over the place as one of the best aerobatic planes, but a Yak 52?  Well, it really comes down to the first time I was really exposed to this plane, and that was in one of my, and my oldest daughter's, favorite movies: Resident Evil: Afterlife.  In the beginning of this movie Alice (Milla Jovavich) along with Claire (Ali Larter), flies a Yak 52 from Alaska to Los Angeles and crash lands it on top of a sky scrapper.  First you may ask, "How did I even notice the plane with Milla Jovavich and Ali Larter?  Well I did and I fell in love with Milla,.. I mean the Yak 52 and have liked this quirky plane ever since.  I most likely would not be scratch building this plane except that it's really hard to find a Yak 52 kit, especially for electric.  So, I'm building my own.

How am I starting?

Like Daniel suggests, I'm starting with a "three view".  This is like it sounds, a drawing with three views of the subject.  I found several just by searching the Internet for "Yak 52" and "drawing", "plans", "three view", etc.  After selecting the one I liked the most, I had to figure how big I wanted to make it and how I was going to scale it up.  I could have used Daniel's technique of finding all of the "joints" and scaling and transferring  all of these measurements to a larger sheet, but I have laser printers and computers at my disposal and decided to use them to scale the drawing.  I started by deciding that I would like to make mine 5 times larger than my drawing.  This would give me about a 33 inch wing span.  The drawing I had was already sized for an 8.5 x 11 sheet of paper so once I opened it in my drawing program, I selected a custom paper size of 5 times 8.5 x 11 ( or at least 42.5 x 55 inches in my case).  Then I expanded my drawing dimensions by a factor of 5 in height and width.  From here I saved the new drawing as a PDF file.  From my PDF document viewer I had the option to print on multiple sheets of letter paper or, "Poster" print.  This then gave me a bunch of sheets that I cut out and taped together.

My enlarged drawing "Poster" printed and all taped together

Now, on to the build!

I started the same way that Daniel did with his planes that used bulkhead sections.  I started with a fuselage base to attach sections to.  I also started by normalizing and straightening some of the dimensions.  By this I mean that I took out some of the subtle curves and contours and also adjusted some of the dimensions to even increments.  The width of the fuselage base in the photo was set to an even 3 inches instead of the measured 3 and 1/16 inches.  I also had to estimate where the firewall would go and what I would make it from and how thick that would be (I decided on 1/8 inch plywood).

Then I started drawing out bulkhead pieces and shaping them down to compensate for the 3/16 inch foam skin I'm going to wrap it in.  I had some nice sectional views to work with that you can see in the previous photo.  These helped greatly in getting the shape right.  If I did not have these I would have been tempted to just make it completely round the whole length like I have seen other do.

 Here I have all of my sections cut out and trimmed for the skin and the center section removed (the lines through the middle in the above photo) to compensate for the fuselage base thickness.  You can see too the bottle of Fabric-Tac glue that I will be using.  I was going to use hot glue for ease and speed, but this was suggested by Daniel Madrigal and others as being lighter and stronger.  The tackiness does help with assembly but it does take overnight to really set up good.

Here we are with all of the bulkhead pieces glued in place ready to start putting in stringers from the nose to the tail.  I'll be using 1/8 x 3/16 basswood strips for this.  I was going to use balsa wood, but the selection I had seemed too soft and flimsy.  I opted for heavier but more strength.




That's all for now.  I'll have more soon.

Thanks for stopping by my blog.  Please feel free to post comments, good or bad, and be sure to come back and check for future posts.

T28 update and putting test equipment to good use

I really wanted to put my test equipment to use and I needed to check out my Airfield T28 with possible BEC/receiver/servo issues.  So I put it all together in this one big post.

This was a complicated subject with all the test equipment and airplane gear so I decided to try my hand at a video post.  So, here goes.

Thank you for watching my video post, let me know how you like this format.

Update to the video:

Further inspection showed that the faulty servo was not the steering servo but the door servo.  In the following photo you can see the bottom servo is the same servo that was over heating in the video.  You can also see that the push rod from the servo is flexed a lot.  This is obviously putting a lot of stress on the servo and is most likely the cause of the current draw.  Something will have to be done about this during the repair.

Stressed servo that failed

I have noticed that the current generation of the Airfield/FMS 1400mm Trojan T28 do not use a servo for these doors but instead uses spring linkage.  I may go this route for this repair and cut one servo from my count.

Thanks for stopping by my blog.  Please feel free to post comments, good or bad, and be sure to come back and check for future posts.

Testing to the rescue

Some times stuff happens and you don't really know why.  This is why you need test equipment.

This was the case with my Dad's new 3D plane.  This was a kit that came without any electronics but had recommendations.  Since it was from Hobby King, of course the recommendations were for their parts.  No big deal, I actually like most of their parts.  I helped my Dad figure out what he needed and what was the best fit of parts from the US warehouse.  When he got everything together he noticed that things were getting hot.  Not a good sign.

He had a good idea of how to put a heat sink on his speed controller, since this is what was getting hot, and I helped him figure out the best way to put it on.  What he did was to use some heat sink compound in the center and then some epoxy on the corners to secure it down.  This was of course after cutting away some of the heat shrink to expose the ESC aluminum heat sink.  This is what he ended up with.

Darn good job, don't you think?

This is the other side showing that it is a Hobby King brand 25A (30A burst) variety.  This should already be a pretty good ESC and with the added heat sink, even better.  The velcro in the photo was something he added to help keep the ESC tacked down in his plane (nice idea).

After some testing, it was still getting really hot, too hot to touch and would actually go into shutdown mode!  This already happened once while he was test flying it.  We initially thought he had lost control when it went behind an obstruction, but we no longer think this was the case.

So, now to the testing and test equipment.  I was able to come down with the family and my gear (yes, family comes first. Since there was still some space left in the trunk I could take my gear along!).  We hooked up my power meter in between the battery and the ESC and began testing it out.

We found that at full throttle it was only pulling 14A.  This is well below the rating of 25A, but it was roasting hot after only about 30 seconds.  It even when into shutdown mode about 20 seconds later.  Even with the added heat sink, it was too hot to touch!

We then tested the power draw on my Wild Hawk which I upgraded to a brushless motor with a Turnigy 25A ESC.  This combination drew slightly more current at about 16A, but stayed quite cool and was barely warm after a minute or so of wide open throttle. 

So, this resolved why he lost control.  This also suggests that two other possibilities.  One is that the Hobby King brand parts (or ESC in this case) are not very good, or the other possibility is that they had a batch of much lower rated ESCs go out with the wrong labels on.  We would not have known this without the tester as we would not have been able see that the current draw was well below the rating.

Well, what does he do now?  He has two options.  One is to pursue a replacement from Hobby King and the other is to just go out and buy a more reliable brand.  Since the Hobby King ESC was only about $7, I think he will just look for a better replacement.

Thanks for stopping by my blog.  Please feel free to post comments, good or bad, and be sure to come back and check for future posts.

Can't get enough test equipment

After a long hiatus, I am finally submitting a new post.

Since my last post I have learned a lot about RC equipment and testing.  This has led me to realize that I need another servo tester, or power analyzer.  This one does not control the server under test, but reports on the servo voltage and current use.  This is very important in making sure that servos are up to the task at hand and that the battery or BEC circuit is capable as well.

You may have seen one of my previous posts about my big T28 Trojan and my crash.  I suspected that this crash was due to power issues but have had no way to test this.  With this servo power analyzer I will be able to find out what is going on with the servo/receiver power system.

What is needed for this tester is a way to measure amps and voltage used by a servo, and all the way up to all servos including the receiver.

These are the parts that will be used build my servo power analyzer.

The parts consist of an amp meter, volt meter, project box, small circuit board, connector pins, and some connector lugs.  Also needed but not shown is some wire to make all of the connections.

This is a closer view of the Amp and Volt meters I used.  The Amp meter is rated at 5A max and the Volt meter has a rating of 10 volts.  Most of these testers that I have seen are setup for 500mA and 6 volts.  I chose these values so that I could monitor a larger range of current and voltage.

Another view of the inexpensive (about $6 each including shipping!) meters I bought on eBay.  These are inexpensive, but they'll do just fine.

This is a better view of how the circuit board and pins will be used.  The pins can be snapped off in the number needed.  Since these will be used for servo connections, these will be broken off in 3s.  The circuit board will be cut in half and one half used for each end.

This is how the completed tester looks with the two meters mounted on the face.  The connectors are on each end.

These are the pins for the output or servo side.  I opted to provide two connectors here so I could hook up two servos at a time.  I could also use a splitter cable as well but this was easy enough to add.

This is the input side (sorry for the blurry photo).  There is no need for more than one input here.

This shows a typical setup for testing a servo.  With this setup I can monitor any voltage and current fluctuations while the servo is put through its paces.

The way I plan on using this to test my T28 setup, is to plug the BEC into the input side and the receiver with all of the servo connections into the output side.  Then I will monitor for voltage fluctuations (anything dropping much below 6V) and maximum amp flow.  Anything above the amp rating of the BEC will be a sign that it is not up to the task or I have a problem with a servo or two.

I realize that I did not include a circuit diagram and this would be very helpful for anyone wanting to make one of these.  It's really very basic and should be easy to duplicate.  So, here it is:

The positive voltage path flows through the Amp meter.  The voltage is measured the positive and negative voltage paths.  The servo signal wire passes straight through without interruption.

Thanks for stopping by my blog.  Please feel free to post comments, good or bad, and be sure to come back and check for future posts.